This invention relates generally to display systems for digital oscilloscopes, and in particular to a system for reproducing the envelope of complex signals such as carrier signals. Real-time oscilloscopes provide a continuous time-based display of the instantaneous amplitude values of electrical phenomena, and are thus able to accurately display the waveforms of complex signals, such as high-frequency carrier signals having low-frequency envelopes. These types of waveforms, as well as other types, are also displayable by real-time oscilloscopes equipped with direct-view bistable storage tubes because the signal processing circuits and recording medium are continuous. On the other hand, digital oscilloscopes chop input signals into time points determined by an internal clock, quantize the instantaneous amplitude values at those points, and store the resulting digital representations in a digital memory. The display is regenerated from memory at a predetermined clock rate, and is manifested either as a series of dots, or connected dots. Since the input signals are not functionally related to the internal clock of the digital oscilloscope, whatever the instantaneous value of the input signal happens to be when the clock edge occurs is what gets stored. The information between such points, of course, is lost, so that for complex signals, an intelligible waveform is difficult, if not impossible, to reconstruct.
A method for determining the minimum and maximum amplitude values of repetitive waveforms has now been developed for digital oscilloscopes and is disclosed in co-pending application Ser. No. 61,720, filed July 30, 1979, entitled "Waveform Storage System." It would be desirable to utilize these minimum and maximum values to reproduce the envelope of complex signals.